Structure and Composition of the Universe – Key Vocabulary

20 vocabulary flashcards covering the composition, structure, expansion, and origin theories of the universe.

Universe

All of space-time and its contents, including every form of matter, energy, and the physical laws that govern them.

Baryonic Matter

Ordinary matter made of protons and neutrons (≈4.6 % of the universe); forms atoms, planets, stars, and galaxies.

Cold Dark Matter

Invisible matter that interacts through gravity but not light; thought to bind galaxies together (≈24 % of the universe).

Dark Energy

Mysterious form of energy causing the accelerated expansion of the universe (≈71.4 %).

Galaxy

Massive gravitational system of stars, gas, dust, dark matter, and sometimes a super-massive black hole.

Milky Way

The spiral galaxy that contains our Solar System and hundreds of billions of stars.

Nebula

Large cloud of gas and dust in space; birthplace of stars and planetary systems.

Protostar

Collapsing, rotating core within a nebula that heats up before igniting nuclear fusion to become a star.

Main Sequence Star

Stable, long-lived star (like the Sun) fusing hydrogen to helium in its core; dominates the stellar life cycle.

Redshift

Lengthening of light’s wavelength toward the red end of the spectrum, indicating an object is moving away.

Doppler Effect

Change in a wave’s frequency or wavelength due to relative motion between the source and an observer.

Cosmic Microwave Background (CMB)

Faint, nearly uniform microwave radiation—relic afterglow of the Big Bang—discovered by Penzias and Wilson (1964).

Steady-State Theory

Discredited model claiming the universe has always existed, expands while continuously creating matter to keep density constant.

Big Bang Theory

Prevailing cosmological model stating the universe began ~13.8 billion years ago from a hot, dense singularity and has been expanding since.

Radiation Era

Early phase of the universe when high-energy photons and relativistic particles dominated its dynamics.

Matter Era

Later cosmic phase when matter (dark and baryonic) became dominant, enabling galaxy, star, and planet formation.

Oscillating Universe Theory

Cyclic model proposing successive periods of expansion (Big Bang) and contraction (Big Crunch) repeating forever.

Georges Lemaître

Belgian priest-physicist who first proposed the ‘primeval atom’ hypothesis—precursor to the Big Bang Theory (1927).

Edwin Hubble

Astronomer who discovered galaxy redshifts proportional to distance (1929), providing evidence for an expanding universe.

Abundance of Light Elements

Observed cosmic proportions of hydrogen, helium, and lithium that match Big Bang nucleosynthesis predictions, supporting the theory.